Lecture 25 (Cut off for Exam 2) Flashcards
ANS
Autonomic Nervous System (ANS)
Part of nervous system that controls or maintains visceral functions
Vegatative System
Parasympathetic Nervous System (PNS) - Cranial Sacral Region (discrete responses)
Fight or Flight
Sympathetic Nervous System (SNS) - Thoracic Lumbar Region (diffuse responses)
Autonomic
Involuntary
Somatic
Voluntary
Primary Roles of ANS
- Homeostasis - maintenance of constant, internal environment
- Achieved by regulation of digestive, circulation, respiration, excretion, reproduction,p and temperature
- Controlled by smooth muscle, glands, and cardiac muscle
- Provide appropriate and coordinated responses to external stimuli (response to meal, fight, extreme temps)
Pharmacologic CNS
Catecholamines, Acetylcholine, & Numerous other Neurotransmitters
Parts of Peripheral NS
- Autonomic NS
- Somatic NS
Pharmacologic ANS
Ganglionic Acetylcholine & Nicotinic Receptors
Pharmacologic SNS
Acetylcholine & Nicotinic Receptors
Parts of ANS
- Sympathetic
- Parasympathetic
Serves same organs mostly, but with antagonistic effects
Pharmacologic Sympathetic
Catecholamine (DA, NE, EPI) Receptors
Pharmacologic Parasympathetic
Acetylcholine & Muscarinic Receptors
ANS
- Not under conscious control
- Cells originate in ventral or intermediate horn
- Myelinated axon of 1st neuron leaves CNS to synapse with second, ganglion neuron
- Second neuron is unmyelinated and does to organ it serves
Somatic NS
- Voluntary Control
- Motor neurons originate in ventral horn
- Extends directly to innervate skeletal muscle
Parasympathetic NS
- Rest and digestion
- Salivation
- HCl secretion
- GI propulsion
- Urination
Sympathetic NS
- Fight or Flight
- O2 intake
- Increased heart rate and contractility
- BP
- Increased blood flow to brain, heart, and muscles
- Liver gluconeogenesis and glycogenolysis
Parasympathetic Cranial Nerve Outflow
- III - pupils constrict
- VII - tears, nasal mucus, saliva
- IX - parotid salivary gland
- X - Vagus nerve
Vagus Nerve (X)
- Organs or thorax/abdomen
- Stimulates digestive glands (acid)
- Increases motility of smooth muscle in digestive tract
- Decreases heart rate (may cause bradycardia)
- Causes bronchial constriction
Parasympathetic Sacral Nerve Outflow
- Form pelvic splanchnic nerves
- Supply 2nd half of large intestine
- Supply all pelvic (genitourinary) organs
Sympathetic Innervation
- Diffusion response
- Sympathetic ONLY: sweat glands, hair on skin, blood vessels (constriction and dilation, catecholamines)
Sympathetic + Parasympathetic Innervation
- Liver gluconeogenesis and glycogenolysis
- Increased heart rate and contractility
- Increased respiratory rate
- Dilate bronchi
- Dry mouth
- Pupils dilating
Visceral Reflex Arcs
-Combination of visceral sensory and autonomic nerves
-Many spinal reflexes like defecation and urination
EX: “enteric” NS: 2-3 neuron reflex arcs within gut wall
Central Control of ANS
- Amygdala
- Hypothalamus
- Reticular Formation
Amygdala
- Maintain limbic region for emotions
- Stimulates sympathetic activity, especially previously learned fear-related behavior
Hypothalamus
Main integration center
Reticular Formation
- Most direct influence over autonomic function
- Norepinephrine (NE) containing brain stem nuclei control many functions of ANS - Locus Coeruleus (NE) and Nucleus Tractus Solitarius (Epinephrine (EPI))
PNS Functional Considerations
- Purpose = conserve and restore energy, essential for life, maintain organ function
- Most actions are mediated by muscarine M3 receptors (except decreased heart rate which is M2), mediated by PNS
- Localized, discrete actions, NOT massive response
- Less divergence than SNS, ACh = short action
- Widespread PNS is NOT beneficial
SLUD Response
- Salivation, lacrimation, urination, defecation
- ACh also released at ganglion and muscle cholinergic transmission with nicotine receptors and different agonist/antagonists
SNS Functional Considerations
- Stimulate activities that expend energy in response to fear, anger, stress, etc.
- Not needed for life but maintain BP, temperature, etc.
- Transmit actions via catecholamine neurotransmitters via specific receptors like NE, EPI, and dopamine (DAT)
Beta-1 Receptor Actions
- Increased heart rate
- Renin release
Alpha-1 Receptor Actions
- Increased blood pressure
- Decreased blood to skin, internal regions
- Pupil dilation (mydriasis)
- Piloerection
Beta-2 Receptor Actions
- Increase blood to skeletal muscle
- Increase blood glucose
- Dilate bronchioles
- Accommodate for far vision
Exceptions to Dual Innervation
- Sweat glands - sympathetic control, mediated by ACh muscarinic receptors
- Renal Vasculature - sympathetic, mediated dopamine mechanism (vasodilation)
- Blood vessels - only sympathetic innervation (some parasympathetic innervation but muscarinic receptors that mediate vasodilation)
Transmission
Passage of impulse across across a synapse or neuroeffector junction
Neurotransmission in ANS
- Exocytosis - electrogenic (action potential induced) opens calcium channels and release vesicle contents in synaptic cleft
- Entering calcium causes VAMP to interact with SNAP in the terminal membrane
- Vesicles fuse to membrane and release neurotransmitters
- Produces response by binding to post/pre-synaptic receptors
ANS - Site of Regulation
- Presynaptic Autoreceptors - neuronal receptors that response to the neuron’s own transmitters to modulate neurotransmitter release (positive/negative feedback)
- Alpha-2 receptors - inhibitory autoreceptors on NE neurons and inhibitory heteroreceptors on ACh neurons
- Alpha-2 agonists - Decrease NE & ACh release
- Alpha-2 antagonists - Increase NE & ACh release
- Presynaptic ACh autoreceptors: muscarinic (inhibitory) & nicotonic (excitatory)
- Anaxonic interactions - one presynaptic terminal alters the neurotransmitter release of another presynaptic terminal
Synaptic Vesicle Regulation
- VAMP - involved with vesicle transport and exocytosis
- Reserpine - binds to VMAT2 and prevents uptake/storage of monoamine (catecholamine and serotonin) in vesicles which depletes monoamines
- Tetanus/Botulism Toxin - bind to VAMP and inhibit vesicle release causing a decrease in ACh function and post synaptic receptors
Terminating Neurotransmitter Action - ACh
- ACh - rapidly metabolized by ACh-erase at synaptic clefts, produces choline and acetate
- Choline is taken up into neuron and reutilized
Terminating Neurotransmitter Action - Catecholamine
-Rapidly removed by uptake transporters in presynaptic terminal
Terminating Neurotransmitter Action - DAT & NE
-Transporters for these ligands have been cloned and localized to comparable neurons
Uptake Inhibitors
-Used therapeutically
EX: Antidepressants, cocaine, amphetamine
Main end point of SNS & ANS
Muscle contraction or relaxant
Skeletal Muscles
- Attached to bone, usually in pairs to antagonize joint movement
- VOLUNTARY or volitional muscle that the individual controls
- Striated due to myofibrils that have thick and thin filaments
Smooth Muscle
- GI tract, blood vessels, bladder, bronchiole tubes, uterus, prostate
- Cells are spindle shaped, no striations
- Involuntary and controlled by ANS
Cardiac Muscle
- Myocardium, striated but involuntary
- Heart controls own activity (SA/AV nodes) but influenced by ANS
- Myocytes are connected by tight membrane and gap junctions that function as a unit
